Fill with the "window" color of the palette as passed in through
the style option, which takes care of active vs inactive color
selection.
The title bar of a docked dockwidget is a bit lighter than the
main window title and unified toolbar background, but identical
to the color of the title of an undocked dock widget. This is now
the case for both dark mode and light modes.
Also remove the gradient fill from the status bar, just fill it
with the window brush.
Remove the now unused helper functions for the title bar
gradient.
Fixes: QTBUG-92855
Pick-to: 6.7
Change-Id: Ia04c630201b288c0107567d3f459f66129693c82
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>
0d91cc866f